Polyurethane elastomers are well known for use in making shaped articles of manufacture. Methods of making polyurethane elastomers are disclosed for example in U.S. Pat. No. 4,476,292 and U.S. Pat. No. 2,969,386. Such shaped articles of manufacture include tough wear-resistant parts, foundry patterns, core boxes, impact pads for railroad draft gears, dye pads for metal forming punch presses and a variety of shaped mechanical rubber-like components such as shock mitigation pads.
Another important group of shaped articles made from polyurethane elastomers includes electrically biasable parts for use in electrophotographic copying equipment, such as transfer rollers and transfer belts. Such transfer rollers and belts cooperate electrically with a photoconductive surface to establish a directional force field between the transfer roller or belt and the photoconductive surface. The direction of the force field assists in moving a toner-developed photoconductive image from the photoconductive surface to the transfer roller or belt. Subsequently the direction of the force field is reversed so that the image now residing on the transfer roller or belt can be transferred to a more permanent surface such as paper.
Transfer rollers, belts and other electrically biased shaped articles used in electrophotographic equipment are described in great detail in U.S. Pat. No. 3,959,573 and U.S. Pat. No. 3,959,574.
U.S. Pat. No. 3,959,574 describes transfer rollers and belts made from polyurethane elastomers wherein the polyurethane elastomer contains additives designed to establish a certain level of resistivity in the elastomers. The additives according to the patent must be soluble in or dispersible in the polyurethane elastomer. The additives are worked into the polyurethane by direct melting of the additive into the polyurethane or incorporating a solution or dispersion of the additive into the polyurethane. The problem is that over time the additives, for various reasons, are leached out of the elastomer. This results in a decline in the level of conductivity in polyurethane elastomers.